This invention relates to a screen opening and shutting drive device applied to, for example, a case where curtains arranged leftward and rightward are opened or shut in the mutually opposite direction, or where blinds arranged on the upper part of a window frame are opened or shut upward and downward.
The applicant has already developed a screen opening and shutting drive device.
The device is designed such that planetary gear mechanisms are installed between a drive source such as a motor, and an output pulley, internal gears of the planetary gear mechanisms are rotatably supported in a given range, the motor is driven by starting switches, and the internal gear is rotated by a load reaction that a curtain bears at a travel terminal, which in turn causes a stopping switch for the drive source to be operated.
Of course, the starting switches are operable for the curtain opening and shutting sides, and two stopping switches are provided in the curtain opening and shutting sides to be activated in a circuit as shown in FIG. 3.
This means that the circuit includes a curtain opening starting switch 38b, a curtain shutting starting switch 38a, reversible motor 16, a curtain opening stopping switch 33b, and a curtain shutting stopping switch 33a.
With this device, for example, when the curtain is at a position of opening with the curtain opening stopping switch 33b operated off by the internal gear, and in order to shut the curtain from the state, the starting switch 38a is operated on to drive the motor 16 to the shutting position, the opening stopping switch 33b remains operated off, thus it is necessary to set the internal gear at the neutral state and to drive the curtain to the shutting position.
This necessity results from an inconvenience that if the curtain opening stopping switch remains off as described previously when an attempt to return the curtain to the opening position is made in the course of the curtain travel to the shutting position, the motor 16 will fail to rotate to the curtain opening position.
The operation to return to the neutral state is performed by rotating the internal connecting element at the early drive stage of the motor 16 to set the gear at the neutral state, which is effected by a travel resistance of the curtain and a torque load of the drive system.
However, the rotation has an unfavorable factor that the internal connecting element may perform an unstable operation such that it does not rotate at times since it is not forcefully rotated.